<template>
  <div>
    <div class="list">
      <div
        class="item"
        v-for="item in letters"
        :key="item"
        :ref="item"
        @click="handleItemClick"
        @touchstart.prevent="handleTouchStart"
        @touchmove="handleTouchMove"
        @touchend="handleTouchEnd"
      >{{item}}</div>
    </div>
  </div>
</template>
<script>
export default {
  name: 'cityAlpha',
  props: {
    cities: Object
  },
  data () {
    return {
      touchStatus: false,
      startY: 0,
      timer: null
    }
  },
  computed: {
    letters () {
      const letters = []
      for (let i in this.cities) {
        letters.push(i)
      }
      return letters
    }
  },
  updated () {
    this.startY = this.$refs['A'][0].offsetTop
  },
  methods: {
    handleItemClick (e) {
      this.$emit('change', e.target.innerHTML)
    },
    handleTouchStart () {
      this.touchStatus = true
    },
    handleTouchMove (e) {
      if (this.timer) {
        clearTimeout(this.timer)
      }
      this.timer = setTimeout(
        () => {
          if (this.touchStatus) {
            const touchY = e.touches[0].clientY - 79
            const index = Math.floor((touchY - this.startY) / 20)
            if (index >= 0 && index <= this.letters.length) {
              this.$emit('change', this.letters[index])
            }
          }
        }, 16
      )
    },
    handleTouchEnd () {
      this.touchStatus = false
    }
  }
}

</script>
<style lang="stylus" scoped>
@import '~styles/varibles.styl';

.list {
  display: flex;
  flex-direction: column;
  justify-content: center;
  position: absolute;
  right: 0;
  bottom: 0;
  width: 0.4rem;
  top: 1.58rem;

  .item {
    line-height: 0.4rem;
    text-align: center;
    color: $bgColor;
  }
}
</style>
